1. Field of the Invention
The present invention relates to a rechargeable battery, and more particularly, to a rechargeable battery that can simplify a manufacturing process and improve the capacity of the battery, in comparison with a conventional rechargeable battery.
2. Description of the Related Art
Generally, a rechargeable battery can be used repeatedly if the rechargeable battery is charged, unlike a disposable battery. The rechargeable battery has been used mainly as a power source for electronic devices used for communication, for information processing, and for multimedia. Since a rechargeable battery is a power source having ultra-light weight, high energy density, high output voltage, low self-electric discharge rate, environmental friendly properties and long lifetime, interest in rechargeable batteries has been recently become intensified and rapidly developed.
The rechargeable battery can be classified into either a Nickel-Metal Hydride (Ni-MH) battery or a Lithium-ion (Li-ion) battery, depending upon th electrode active material. Particularly, the Lithium-ion battery can be classified into one of two categories according to the type of electrolyte: one category of Lithium-ion battery uses a liquid electrolyte and the other category uses a solid polymer electrolyte or a gel state electrolyte. Further, the Lithium-ion battery can be classified into various types such as a can type or a pouch type according to the shape of a container receiving the electrode assembly.
The Lithium-ion battery is much higher in energy density per weight than the disposable battery so as to realize its characteristic as an ultra-light battery. The average voltage per cell of the Lithium-ion battery is 3.6V, which is equal to three times of the average voltage of any other rechargeable battery, such as Nickel-Cadmium battery and Nickel-Metal Hydride (Ni-MH) battery. In addition, the Lithium-ion battery has a self electric discharge rate of less than about 5% per a month at 20° C., which is about ⅓ of the rate of a Ni—Cd battery or a Ni-MH battery. Moreover, the Lithium-ion battery is environmental friendly because Lithium-ion batteries do not use a heavy metal such as Cadmium or Mercury, and further because a Lithium ion battery has the ability to charge and discharge for approximately 1,000 times in steady state. Therefore, the Lithium-ion battery has rapidly developed with concomitantly with recent progress in information and communication technology.
The Lithium-ion battery is formed by disposing an electrode assembly which is composed of an anode plate, cathode plate and separator and which is laminated and wound, inside a can made from aluminum or aluminum alloy, filled with an electrolytic solution, and tightly sealed along the upper opening of the can by a cap assembly.
The reason for forming the can from aluminum or aluminum alloy is that the weight of the aluminum is lighter than iron or any of the other electrically conductive metals and therefore it is possible to make the battery lightweight, and the aluminum would not corrode even when the battery has been used for a long time. Such a Lithium-ion battery usually has the electrode terminal which is electrically isolated from the can and the electrode terminal becomes one pole of the battery. Meanwhile, the can which encases the battery becomes the other pole.
Meanwhile, the Lithium-ion battery may be exposed to a danger of explosion by a sudden increase in the voltage in the cases of an external short-circuit, an internal short-circuit by a mechanical impact, or an over-charge/over-discharge. To avoid such a danger, the Lithium ion battery is normally disposed inside a battery pack which is electrically connected to a safety device such as a positive temperature coefficient (PTC) element, a thermal fuse and a protection circuit module. Meanwhile, the safety device is coupled to either an anode electrode or a cathode electrode of a bare cell using a conductor, which is so-called a lead plate. The bare cell is a battery in a state where a cap assembly is coupled with a can into which an electrode assembly is inserted. In other words, the bare cell shows the state of the rechargeable battery before the rechargeable battery is formed as either a cylindrical type battery pack, or an angular type battery pack, or a pouch type battery pack. The safety device creates an electrical open circuit that interrupts the flow of an electric current when the battery temperature reaches a high level or when the battery voltage suddenly increases by an over-charge, or when an over-discharge of the battery occurs, so as to prevent the battery from being broken.
The battery pack can be classified into two types: either a hard pack battery or an inner pack battery, according to the external shape of the battery pack. In the hard pack battery, a plastic resin housing is integrally molded on the outside the battery in a state where the external terminal that is to be electrically connected to an external device is exposed. In an inner pack battery, a plastic resin housing is not molded on the outside the battery in a state where an external terminal is exposed. Generally, when a hard pack battery is mounted on an external device, because a part of outer surface of the housing of the hard pack battery is exposed, at least one part of the outer surface of the housing of the hard pack battery which is exposed is composed of the same material as the housing of the external device. Therefore, the hard pack battery may be mounted easily on the external device. The housing of the battery has a problem, however, because the housing must be produced to have a structure that is suitable for the shape and the structure of the external device. On the other hand, for the inner pack battery, because an extra decoration is attached to the case when the inner pack battery is mounted on the external device, the loading process of the inner pack battery is troublesome in comparison to the hard pack battery. But, the inner pack battery advantageously may be used regardless of the shape or structure of the external device. Therefore, the development of the inner pack battery, which can be employed regardless of the shape and a structure of external device, has recently been emphasized.
The bare cell is usually constructed with an anode terminal and a cathode terminal on a side opposite to a protective circuit board. The anode terminal is a cap plate made from aluminum or aluminum alloy, and the cathode terminal is a terminal extended from the cap plate like a protrusion and electrically isolated from the cap plate by an insulating gasket disposed around the circumference of the cathode terminal.
The protective circuit board is constructed with a circuit formed on a panel made from resin, and an external terminal is positioned on an outside surface. The circuit borne by the circuit board is formed on a back side of the protective circuit board, i.e., on the inside surface of the protective circuit board. In addition, the lead plate is located between the bare cell and the protective circuit board so as to be electrically connected between the bare cell and the protective circuit board. That is, the cap plate of the bare cell and the protective circuit board are electrically connected by an anode lead plate, and the electrode terminal of the bare cell and the protective circuit board are electrically connected by a cathode lead plate. In addition, the protective circuit board is attached to the bare cell by melting of a molding resin after the protective circuit board has been electrically connected to the bare cell.
The lead plate is generally formed in an ‘L’-shape. One surface of the lead plate is attached to the bare cell and the other surface is attached to the protective circuit board. Accordingly, the distance between the bare cell and the protective circuit board is equal to the length of the lead plate itself Accordingly, the longitudinal size of the battery is increased, reducing the capacity per volume of the battery.
In addition, the protective circuit board and other accessories of the battery are made from a molding resin, whereas the cap plate and the can of the bare cell are made from a metal like material. When forming the battery by connecting the protective circuit board attached to the bare cell, the contact area between the molding resin part and the bare cell is not large. Therefore, the battery may be easily twisted or bent by an external force.
That is, if the molding resin part is twisted about the bare cell beyond a certain angle, the electrical connection between the anode terminal or the cathode terminal of the bare cell and the external terminal of the protective circuit board through the lead plate may be unstable, even when the molding resin part is not completely broken. In addition, the safety devices of the battery may not to operate normally.
In addition, the method of combining the molding resin part by the melting method is problematical because the manufacturing process is complicated and the cost is high. Therefore, the productivity becomes low.